Process for the production of L-amino acids by fermentation using coryneform bacteria with an attenuated mqo gene

ABSTRACT

A process for the production of an L-amino acid wherein coryneform bacteria (e.g.  Coryneform glutamicum ) in which expression of the mqo gene coding for malate quinone oxidoreductase is attenuated are fermented to produce a desired amino acid, and the amino acid is concentrated in the medium or cells and isolated. Optionally, further genes in the biosynthetic pathway of the desired amino acid are enhanced, and/or metabolic pathways that reduce formation of the amino acid are suppressed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to German application DE 101 17 816.6,filed Apr. 10, 2001, and U.S. Provisional application No. 60/352,212,filed Jan. 29, 2002, each of which is incorporated herein by referencein its entirety.

FIELD OF THE INVENTION

The invention provides a process for the production of L-amino acids,especially L-lysine, by fermentation using coryneform bacteria in whichthe mqo gene, which codes for malate quinone oxidoreductase, has beenattenuated.

BACKGROUND INFORMATION

L-amino acids, especially L-lysine, are used in human medicine and inthe pharmaceuticals industry, in the foodstuffs industry and, veryespecially, in the feeding of animals.

It is known that amino acids are produced by fermentation of strains ofcoryneform bacteria, especially Corynebacterium glutamicum. Because oftheir great importance, attempts are continuously being made to improvethe production processes. Improvements to the processes may concernmeasures relating to the fermentation, such as, for example, stirringand oxygen supply, or the composition of the nutrient media, such as,for example, the sugar concentration during the fermentation, or workingup to the product form by, for example, ion-exchange chromatography, orthe intrinsic performance properties of the microorganism itself.

In order to improve the performance properties of such microorganisms,methods of mutagenesis, selection and mutant selection are employed.Such methods yield strains which are resistant to antimetabolites, suchas, for example, the lysine analogue S-(2-aminoethyl)-cysteine, or areauxotrophic for metabolites that are important in terms of regulation,and which produce L-amino acids.

For a number of years, methods of recombinant DNA technology have alsobeen used for improving the strain of L-amino acid-producing strains ofCorynebacterium glutamicum, by amplifying individual amino acidbiosynthesis genes and studying the effect on L-amino acid production.

SUMMARY OF THE INVENTION Object of the Invention

In EP-A-1038969 it is described that an improvement in the production ofL-amino acids by fermentation can be achieved by enhancement, especiallyoverexpression, of the mqo gene.

The inventors have set themselves the object of providing novel basesfor improved processes for the production of L-amino acids, especiallyL-lysine, by fermentation using coryneform bacteria.

DESCRIPTION OF THE INVENTION

Where L-amino acids or amino acids are mentioned hereinbelow, they areto be understood as meaning one or more amino acids, including theirsalts, selected from the group L-asparagine, L-threonine, L-serine,L-glutamate, L-glycine, L-alanine, L-cysteine, L-valine, L-methionine,L-isoleucine, L-leucine, L-tyrosine, L-phenylalanine, L-histidine,L-lysine, L-tryptophan and L-arginine. L-lysine is particularlypreferred.

Where L-lysine or lysine is mentioned hereinbelow, it is to beunderstood as meaning not only the bases but also the salts, such as,for example, lysine monohydrochloride or lysine sulfate.

The invention provides a process for the production of L-amino acids byfermentation using coryneform bacteria in which at least the nucleotidesequence coding for malate quinone oxidoreductase (mqo gene) isattenuated, especially excluded or expressed at a low level.

This invention also provides a process for the production of L-aminoacids by fermentation in which the following steps are carried out:

-   -   a) fermentation of the L-amino acid-producing coryneform        bacteria in which at least the nucleotide sequence coding for        malate quinone oxidoreductase is attenuated, especially excluded        or expressed at a low level;    -   b) concentration of the L-amino acids in the medium or in the        cells of the bacteria; and    -   c) isolation of the desired L-amino acids, in which optionally        portions or the entirety of the constituents of the fermentation        liquor and/or of the biomass remain in the end product.

The strains used preferably produce L-amino acids, especially L-lysine,even before attenuation of the mqo gene.

Preferred embodiments are to be found in the claims.

The term “attenuation” or “attenuate” in this context describes thediminution or exclusion of the intracellular activity of one or moreenzymes (proteins) in a microorganism that are coded for by thecorresponding DNA, by, for example, using a weak promoter or using agene or allele that codes for a corresponding enzyme having a low levelof activity, or by inactivating the corresponding gene or enzyme(protein), and optionally by combining those measures.

The microorganisms provided by the present invention are able to produceamino acids from glucose, saccharose, lactose, fructose, maltose,molasses, starch, cellulose or from glycerol and ethanol. They may berepresentatives of coryneform bacteria, especially of the genusCorynebacterium. In the case of the genus Corynebacterium, specialmention may be made of the species Corynebacterium glutamicum, which isknown to those skilled in the art for its ability to produce L-aminoacids.

Suitable strains of the genus Corynebacterium, especially of the speciesCorynebacterium glutamicum, are especially the known wild-type strains

-   -   Corynebacterium glutamicum ATCC13032    -   Corynebacterium acetoglutamicum ATCC15806    -   Corynebacterium acetoacidophilum ATCC13870    -   Corynebacterium melassecola ATCC17965    -   Corynebacterium thermoaminogenes FERM BP-1539    -   Brevibacterium flavum ATCC14067    -   Brevibacterium lactofermentum ATCC13869 and    -   Brevibacterium divaricatum ATCC14020        and L-amino acid-producing mutants or strains prepared therefrom        such as, for example, the L-lysine-producing strains    -   Corynebacterium glutamicum FERM-P 1709    -   Brevibacterium flavum FERM-P 1708    -   Brevibacterium lactofermentum FERM-P 1712    -   Corynebacterium glutamicum FERM-P 6463    -   Corynebacterium glutamicum FERM-P 6464    -   Corynebacterium glutamicum ATCC 21513    -   Corynebacterium glutamicum ATCC 21544    -   Corynebacterium glutamicum ATCC 21543    -   Corynebacterium glutamicum DSM 4697 and    -   Corynebacterium glutamicum DSM 5715.

Contrary to the prior art (EP-A-1038969) it has been found thatcoryneform bacteria produce L-amino acids in an improved manner afterattenuation of the mqo gene.

The nucleotide sequence of the mqo gene of Corynebacterium glutamicumhas been published by Molenar et al. (European Journal of Biochemistry254, 395–403 (1998)) and can also be taken from the gene library underAccession Number AJ 22 4946. The nucleotide sequence is also shown inSEQ ID No. 1 and the amino acid sequence of the protein is shown in SEQID No. 2.

The sequences described in the mentioned references coding for malatequinone oxidoreductase can be used according to the invention. It isalso possible to use alleles of malate quinone oxidoreductase, which areformed from the degeneracy of the genetic code or by sense mutationsthat are neutral in terms of function.

In order to achieve attenuation, either the expression of the mqo geneor the catalytic properties of the gene products can be diminished orexcluded. The two measures are optionally combined.

Gene expression can be diminished by carrying out the culturing in asuitable manner or by genetic alteration (mutation) of the signalstructures of gene expression. Signal structures of gene expression are,for example, repressor genes, activator genes, operators, promoters,attenuators, ribosome-binding sites, the start codon and terminators.The person skilled in the art will find information thereon, forexample, in patent application WO 96/15246, in Boyd and Murphy (Journalof Bacteriology 170: 5949 (1988)), in Voskuil and Chambliss (NucleicAcids Research 26: 3548 (1998), in Jensen and Hammer (Biotechnology andBioengineering 58: 191 (1998)), in Pátek et al. (Microbiology 142: 1297(1996)), and in known textbooks of genetics and molecular biology, suchas, for example, the textbook of Knippers (“Molekulare Genetik”, 6thedition, Georg Thieme Verlag, Stuttgart, Germany, 1995) or that ofWinnacker (“Gene und Klone”, VCH Verlagsgesellschaft, Weinheim, Germany,1990).

Mutations that lead to a change in or diminution of the catalyticproperties of enzyme proteins are known from the prior art; exampleswhich may be mentioned are the works of Qiu and Goodman (Journal ofBiological Chemistry 272: 8611–8617 (1997)), Sugimoto et al. (BioscienceBiotechnology and Biochemistry 61: 1760–1762 (1997)) and Möckel (“DieThreonindehydratase aus Corynebacterium glutamicum: Aufhebung derallosterischen Regulation und Struktur des Enzyms”, Berichte desForschungszentrums Jülichs,Jül-2906, ISSN09442952, Jülich, Germany,1994). Summaries are to be found in known textbooks of genetics andmolecular biology, such as, for example, that of Hagemann (“AllgemeineGenetik”, Gustav Fischer Verlag, Stuttgart, 1986).

There come into consideration as mutations transitions, transversions,insertions and deletions. In dependence on the effect of the amino acidsubstitution on the enzyme activity, missense mutations or nonsensemutations are referred to. Insertions or deletions of at least one basepair in a gene lead to frame shift mutations, as a result of whichincorrect amino acids are incorporated or the translation breaks offprematurely. If a stop codon forms in the coding region as the result ofa mutation, that likewise generally leads to premature breaking off ofthe translation.

Deletions of several codons typically lead to complete loss of enzymeactivity. Instructions for the production of such mutations are part ofthe prior art and can be found in known textbooks of genetics andmolecular biology, such as, for example, the textbook of Knippers(“Molekulare Genetik”, 6th edition, Georg Thieme Verlag, Stuttgart,Germany, 1995), that of Winnacker (“Gene und Klone”, VCHVerlagsgesellschaft, Weinheim, Germany, 1990) or that of Hagemann(“Allgemeine Genetik”, Gustav Fischer Verlag, Stuttgart, 1986).

The invention provides the allele 672, shown in SEQ ID No. 3, of the mqogene, which allele carries the nucleotide adenine instead of thenucleotide guanine at position 672 of the DNA sequence (see SEQ ID No.1), which leads to substitution of the TGG codon coding for the aminoacid tryptophan-224 (see SEQ ID No. 2) by an opal (TGA) stop codon.

The invention also provides the allele 1230, shown in SEQ ID No. 4, ofthe mqo gene, which allele carries the nucleotide adenine instead of thenucleotide guanine at position 672 of the DNA sequence (see SEQ ID No.1), which leads to substitution of the tgg codon coding for the aminoacid tryptophan-224 (see SEQ ID No. 2) by an opal stop codon and whichadditionally carries a nucleotide substitution at position 1230 ofcytosine to thymine.

A common method of mutating genes of C. glutamicum is the method of genedisruption and of gene replacement described by Schwarzer and Pü{umlautover (h)}ler (Bio/Technology 9, 84–87 (1991)).

In the method of gene disruption, a central portion of the coding regionof the gene in question is cloned into a plasmid vector which is able toreplicate in a host (typically E. coli), but not in C. glutamicum.Suitable vectors are, for example, pSUP301 (Simon et al., Bio/Technology1, 784–791 (1983)), pK18mob or pK19mob (Schäfer et al., Gene 145, 69–73(1994)), pK18mobsacB or pK19mobsacB (Jäger et al., Journal ofBacteriology 174: 5462–5465 (1992)), pGEM-T (Promega corporation,Madison, Wis., USA), pCR2.1-TOPO (Shuman (1994). Journal of BiologicalChemistry 269:32678–32684; U.S. Pat. No. 5,487,993), pCR®Blunt(Invitrogen, Groningen, Netherlands; Bernard et al., Journal ofMolecular Biology, 234: 534–541 (1993)) or pEM1 (Schrumpf et al., 1991,Journal of Bacteriology 173:4510–4516). The plasmid vector containingthe central portion of the coding region of the gene is then transferredto the desired strain of C. glutamicum by conjugation or transformation.The method of conjugation is described, for example, in Schäfer et al.(Applied and Environmental Microbiology 60, 756–759 (1994)). Methods oftransformation are described, for example, in Thierbach et al. (AppliedMicrobiology and Biotechnology 29, 356–362 (1988)), Dunican and Shivnan(Bio/Technology 7, 1067–1070 (1989)) and Tauch et al. (FEMSMicrobiological Letters 123, 343–347 (1994)). After homologousrecombination by means of a cross-over occurrence, the coding region ofthe gene in question is disrupted by the vector sequence, and twoincomplete alleles lacking the 3′- and the 5′-end, respectively, areobtained. That method has been used, for example, by Fitzpatrick et al.(Applied Microbiology and Biotechnology 42, 575–580 (1994)) to excludethe recA gene of C. glutamicum.

In the gene replacement method, a mutation, such as, for example, adeletion, insertion or base substitution, is produced in vitro in thegene in question. The allele that is produced is in turn cloned into avector that is not replicative for C. glutamicum, and the latter is thentransferred to the desired host of C. glutamicum by transformation orconjugation. After homologous recombination by means of a firstcross-over occurrence effecting integration and by means of a suitablesecond cross-over occurrence effecting an excision in the target gene orin the target sequence, incorporation of the mutation or of the alleleis achieved.

That method has been used, for example, by Peters-Wendisch et al.(Microbiology 144, 915–927 (1998)) to exclude the pyc gene of C.glutamicum by means of a deletion. That method has been used by Schäferet al. (Gene 145: 69–73 (1994)), for example, in order to incorporate adeletion into the hom-thrB gene region. In the same way, a deletion hasbeen introduced into the cgl gene region of C. glutamicum by Schäfer etal. (Journal of Bacteriology 176: 7309–7319 (1994)).

A deletion, insertion or a base substitution can thus be incorporatedinto the mqo gene.

In addition, it may be advantageous for the production of L-amino acids,in addition to attenuating the mqo gene, to enhance, especially tooverexpress, one or more enzymes of the biosynthesis pathway inquestion, of glycolysis, of the anaplerotic pathway, of the citric acidcycle, of the pentose phosphate cycle, of amino acid export, andoptionally regulatory proteins.

The term “enhancement” or “enhance” in this context describes anincrease in the intracellular activity of one or more enzymes orproteins in a microorganism that are coded for by the corresponding DNA,by, for example, increasing the number of copies of the gene or genes,using a strong promoter or a gene or allele that codes for acorresponding enzyme or protein having a high level of activity, andoptionally by combining those measures.

Accordingly, for the production of L-lysine, in addition to attenuatingthe mqo gene, one or more genes selected from the group

-   -   the gene lysC coding for a feed-back resistant aspartate kinase        (Accession No. P26512, EP-B-0387527; EP-A-0699759; WO 00/63388),    -   the gene dapA coding for dihydrodipicolinate synthase (EP-B 0        197 335),    -   the gene gap coding for glyceraldehyde-3-phosphate dehydrogenase        (Eikmanns (1992). Journal of Bacteriology 174:6076–6086),    -   at the same time the gene pyc coding for pyruvate carboxylase        (DE-A-198 31 609),    -   the gene zwf coding for glucose-6-phosphate dehydrogenase        (JP-A-09224661),    -   at the same time the gene lysE coding for lysine export        (DE-A-195 48 222),    -   the gene zwal coding for the Zwal protein (DE: 19959328.0, DSM        13115)    -   the gene tpi coding for triose phosphate isomerase (Eikmanns        (1992), Journal of Bacteriology 174:6076–6086), and    -   the gene pgk coding for 3-phosphoglycerate kinase (Eikmanns        (1992), Journal of Bacteriology 174:6076–6086),        can be enhanced, especially overexpressed.

It may also be advantageous for the production of amino acids,especially L-lysine, in addition to attenuating the mqo gene, at thesame time to attenuate, especially to diminish the expression of, one ormore genes selected from the group

-   -   the gene pck coding for phosphoenol pyruvate carboxy-kinase (DE        199 50 409.1, DSM 13047),    -   the gene pgi coding for glucose-6-phosphate isomerase (U.S. Pat.        No. 6,586,214, DSM 12969),    -   the gene poxB coding for pyruvate oxidase (DE:1995 1975.7, DSM        13114),    -   the gene zwa2 coding for the Zwa2 protein (DE: 19959327.2, DSM        13113).

Finally, it may be advantageous for the production of amino acids, inaddition to attenuating the mqo gene, to exclude undesired secondaryreactions (Nakayama: “Breeding of Amino Acid Producing Microorganisms”,in: Overproduction of Microbial Products, Krumphanzl, Sikyta, Vanek(eds.), Academic Press, London, UK, 1982).

The microorganisms produced according to the invention also form part ofthe invention and can be cultivated, for the purposes of the productionof L-amino acids, continuously or discontinuously by the batch processor by the fed batch or repeated fed batch process. A summary of knowncultivation methods is described in the textbook of Chmiel(Bioprozesstechnik 1. Einführung in die Bioverfahrenstechnik (GustavFischer Verlag, Stuttgart, 1991)) or in the textbook of Storhas(Bioreaktoren und periphere Einrichtungen (Vieweg Verlag,Braunschweig/Wiesbaden, 1994)).

The culture medium to be used must meet the requirements of the strainsin question in a suitable manner. Descriptions of culture media forvarious microorganisms are to be found in the handbook “Manual ofMethods for General Bacteriology” of the American Society forBacteriology (Washington D.C., USA, 1981).

There may be used as the carbon source sugars and carbohydrates, suchas, for example, glucose, saccharose, lactose, fructose, maltose,molasses, starch and cellulose, oils and fats, such as, for example,soybean oil, sunflower oil, groundnut oil and coconut oil, fatty acids,such as, for example, palmitic acid, stearic acid and linoleic acid,alcohols, such as, for example, glycerol and ethanol, and organic acids,such as, for example, acetic acid. Those substances may be usedindividually or in the form of a mixture.

There may be used as the nitrogen source organic nitrogen-containingcompounds, such as peptones, yeast extract, meat extract, malt extract,corn steep liquor, soybean flour and urea, or inorganic compounds, suchas ammonium sulfate, ammonium chloride, ammonium phosphate, ammoniumcarbonate and ammonium nitrate. The nitrogen sources may be usedindividually or in the form of a mixture.

There may be used as the phosphorus source phosphoric acid, potassiumdihydrogen phosphate or dipotassium hydrogen phosphate or thecorresponding sodium-containing salts. The culture medium must alsocontain salts of metals, such as, for example, magnesium sulfate or ironsulfate, which are necessary for growth. Finally, essential growthsubstances, such as amino acids and vitamins, may be used in addition tothe above-mentioned substances. Suitable precursors may also be added tothe culture medium. The mentioned substances may be added to the culturein the form of a single batch, or they may be fed in in a suitablemanner during the cultivation.

In order to control the pH value of the culture, basic compounds, suchas sodium hydroxide, potassium hydroxide, ammonia or ammonia water, oracid compounds, such as phosphoric acid or sulfuric acid, areexpediently used. In order to control the development of foam,anti-foams, such as, for example, fatty acid polyglycol esters, may beused. In order to maintain the stability of plasmids, suitablesubstances having a selective action, such as, for example, antibiotics,may be added to the medium. In order to maintain aerobic conditions,oxygen or gas mixtures containing oxygen, such as, for example, air, areintroduced into the culture. The temperature of the culture is normallyfrom 20° C. to 45° C. and preferably from 25° C. to 40° C. The cultureis continued until the maximum amount of the desired product has formed.That aim is normally achieved within a period of from 10 hours to 160hours.

Methods of determining L-amino acids are known from the prior art. Theanalysis may be carried out as described in Spackman et al. (AnalyticalChemistry, 30, (1958), 1190) by anion-exchange chromatography withsubsequent ninhydrin derivatization, or it may be carried out byreversed phase HPLC, as described in Lindroth et al. (AnalyticalChemistry (1979) 51: 1167–1174).

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1: Map of the plasmid pXK99Emob,

FIG. 2: Map of the plasmid pXK99Emobmqo.

The abbreviations and designations used have the following meaning.

Kan: Kanamycin resistance gene aph (3′) -IIa from Escherichia coli BamHICleavage site of the restriction enzyme BamHI HindIII Cleavage site ofthe restriction enzyme HindIII NcoI Cleavage site of the restrictionenzyme NcoI Ptrc trc promoter T1 Termination region T1 T2 Terminationregion T2 lacIq lacIq repressor of the lac operon of Escherichia colioriV Replication origin ColE1 from E. coli mob RP4-mobilization site mqoCloned region of the mqo gene

DETAILED DESCRIPTION OF THE INVENTION

The present invention is explained in more detail in the following usingworking examples.

EXAMPLE 1 Preparation of the Vector pXK99Emobmqo

1.1 Cloning of the mqo gene

From the strain ATCC 13032, chromosomal DNA was isolated by the methodof Eikmanns et al. (Microbiology 140: 1817–1828 (1994)). On the basis ofthe sequence of the mqo gene known for C. glutamicum, the followingoligonucleotides were chosen for the polymerase chain reaction (see SEQID No. 5 and SEQ ID No. 6):

mqo_oP1: 5′- GA GGA TCC GCA GAG AAC TCG CGG AGA TA-3′ mqo_hind: 5′-CT AAG CTT CGT AGC GAG CCT TGA TGT AT-3′

The primers were chosen here so that the amplified fragment contains theincomplete gene, starting with the native ribosome binding site withoutthe promoter region, and the front region of the mqo gene. Furthermore,the primer mqo_(—oP)1 contains the sequence for the cleavage site of therestriction endonuclease BamHI, and the primer mqo_hind the cleavagesite of the restriction endonuclease HindIII, which are marked byunderlining in the nucleotide sequence shown above.

The primers shown were synthesized by MWG-Biotech AG (Ebersberg,Germany) and the PCR reaction was carried out by the standard PCR methodof Innis et al. (PCR protocols. A guide to methods and applications,1990, Academic Press) with Pwo-Polymerase from Roche Diagnostics GmbH(Mannheim, Germany). With the aid of the polymerase chain reaction, theprimers allow amplification of a DNA fragment 468 bp in size, whichcarries the incomplete mqo gene, including the native ribosome bindingsite.

The mqo fragment 468 bp in size was cleaved with the restrictionendonucleases BamHI and HindIII and then isolated from the agarose gelwith the QiaExII Gel Extraction Kit (Product No. 20021, Qiagen, Hilden,Germany).

1.2 Construction of the Vector pXK99Emob

The IPTG-inducible expression vector pXK99Emob was constructed accordingto the prior art. The vector is based on the Escherichia coli expressionvector pTRC99A (Amann et al., Gene 69: 301–315 (1988)) and contains thetrc promoter, which can be induced by addition of the lactose derivativeIPTG (isopropyl β-D-thiogalactopyranoside), the termination regions T1and T2, the replication origin ColE1from E. Coli, the lacI^(q) gene(repressor of the lac operon from E.coli), a multiple cloning site (mcs)(Norrander, J. M. et al. Gene 26, 101–106 (1983)), the kanamycinresistance gene aph(3′)-IIa from E. coli (Beck et al. (1982), Gene 19:327–336) and the RP4-mobilization-site from the cloning vectorpK18mobsacB (Schaefer et al, Gene 14: 69–73 (1994).

It has been found that the vector pXK99Emob is quite specificallysuitable for regulating the expression of a gene, in particulareffecting attenuated expression in coryneform bacteria. The vectorpXK99Emob is an E. coli expression vector and can be employed in E. colifor enhanced expression of a gene.

Since the vector cannot replicate independently in coryneform bacteria,this is retained in the cell only if it is integrated into thechromosome. The peculiarity of this vector here is the use for regulatedexpression of a gene after cloning of a gene section from the frontregion of the corresponding gene in the vector containing the startcodon and the native ribosome binding site, and subsequent integrationof the vector into coryneform bacteria, in particular C. glutamicum.Gene expression is regulated by addition of metered amounts of IPTG tothe nutrient medium. Amounts of 0.5 μM up to 10 μM IPTG have the effectof very weak expression of the corresponding gene, and amounts of 10 μMup to 100 μM have the effect of a slightly attenuated to normalexpression of the corresponding gene.

The E. coli expression vector pXK99Emob constructed was transferred bymeans of electroporation (Tauch et al. 1994, FEMS Microbiol Letters,123: 343–347) into E. coli DH5αmcr (Grant, 1990, Proceedings of theNational Academy of Sciences U.S.A., 87:4645–4649). Selection of thetransformants was carried out on LB Agar (Sambrook et al., MolecularCloning: A Laboratory Manual. 2^(nd) Ed., Cold Spring Harbor LaboratoryPress, Cold Spring Harbor, N.Y., 1989), which had been supplemented with50 mg/l kanamycin.

Plasmid DNA was isolated from a transformant by conventional methods(Peters-Wendisch et al., 1998, Microbiology, 144, 915–927), cleaved withthe restriction endonuclease NcoI, and the plasmid was checked bysubsequent agarose gel electrophoresis.

The plasmid construct obtained in this way was called pXK99Emob (FIG.1). The strain obtained by electroporation of the plasmid pXK99Emob inthe E. coli strain DH5αmcr was called E. coli DH5alphamcr/pXK99Emob.

1.3 Cloning of the mqo Fragment into Vector pXK99Emob

The E. coli expression vector pXK99Emob described in Example 1.2 wasused as the vector. DNA of this plasmid was cleaved completely with therestriction enzymes BamHI and HindIII and then dephosphorylated withshrimp alkaline phosphatase (Roche Diagnostics GmbH, Mannheim, Germany,Product Description SAP, Product No. 1758250).

The mqo fragment approx. 458 bp in size described in 1.1, obtained bymeans of PCR and cleaved with the restriction endonucleases BamHI andHindIII was mixed with the prepared vector pXK99Emob and the batch wastreated with T4 DNA ligase (Amersham Pharmacia, Freiburg, Germany,Product Description T4-DNA-Ligase, Code No. 27-0870-04). The ligationbatch was transformed in the E. coli strain DH5αmcr (Hanahan, In: DNAcloning. A Practical Approach. Vol. I, IRL-Press, Oxford, Washington DC,USA). Selection of plasmid-carrying cells was made by plating out thetransformation batch on LB agar (Lennox, 1955, Virology, 1:190) with 50mg/l kanamycin. After incubation overnight at 37° C., recombinantindividual clones were selected. Plasmid DNA was isolated from atransformant with the Qiaprep Spin Miniprep Kit (Product No. 27106,Qiagen, Hilden, Germany) in accordance with the manufacturer'sinstructions and cleaved with the restriction enzymes BamHI and HindIIIto check the plasmid by subsequent agarose gel electrophoresis. Theresulting plasmid was called pXK99Emobmqo. It is shown in FIG. 2.

The following microorganism was deposited as a pure culture on 15^(th)February 2002 at the Deutsche Sammlung für Mikroorganismen undZellkulturen (DSMZ=German Collection of Microorganisms and CellCultures, Braunschweig, Germany) in accordance with the Budapest Treaty:

-   -   Escherichia coli DH5alphamcr/pXK99Emobmqo        (=DH5αmcr/pXK99Emobmqo) as DSM 14815.

EXAMPLE 2 Integration of the Vector pXK99Emobmqo into the genome of theC. glutamicum Strain DSM5715

The vector pXK99Emobmqo mentioned in Example 1 was electroporated by theelectroporation method of Tauch et al.,(1989 FEMS Microbiology Letters123: 343–347) in the strain C. glutamicum DSM5715. The vector cannotreplicate independently in DSM5715 and is retained in the cell only ifit has integrated into the chromosome. Selection of clones withintegrated pXK99Emobmqo was carried out by plating out theelectroporation batch on LB agar (Sambrook et al., Molecular Cloning: ALaboratory Manual. 2_(nd) Ed., Cold Spring Harbor, N.Y., 1989), whichhad been supplemented with 15 mg/l kanamycin and IPTG (1mM).

A selected kanamycin-resistant clone which has the Plasmid pXK99Emobmqo,mentioned in Example 1, inserted in the chromosomal mqo-gene of DSM5715,was called DSM5715::pXK99Emobmqo.

EXAMPLE 3 Preparation of Lysine

The C. glutamicum strain DSM5715::pXK99Emobmqo obtained in Example 2 wascultured in a nutrient medium suitable for the production of lysine andthe lysine content in the culture supernatant was determined. Byaddition of IPTG, attenuated expression of the mqo gene occurs,regulated by the trc promoter.

For this, the strain was first incubated on an agar plate with thecorresponding antibiotic (brain-heart agar with kanamycin (25 mg/l) andIPTG (10 μM)) for 24 hours at 330° C. Starting from this agar plateculture, a preculture was seeded (10 ml medium in a 100 ml conicalflask). The complete medium Cg III was used as the medium for thepreculture.

Medium Cg III NaCl 2.5 g/l Bacto-Peptone 10 g/l Bacto-Yeast extract 10g/l Glucose (autoclaved separately) 2% (w/v) The pH was brought to pH7.4

Kanamycin (25 mg/1) and IPTG (10 μM) were added to this. The preculturewas incubated for 16 hours at 330° C. at 240 rpm on a shaking machine.The OD (660 nm) of the preculture was 0.5. 500 μl of this preculturewere transinoculated into a main culture. By transfer of IPTG-containingmedium from the preculture, the IPTG concentration in the main culturewas approx. 0.5 μM. Medium MM was used for the main culture.

Medium MM CSL (corn steep liquor) 5 g/l MOPS (morpholinopropanesulfonicacid) 20 g/l Glucose (autoclaved separately) 50 g/l Salts: (NH₄)₂SO₄ 25g/l KH₂PO₄ 0.1 g/l MgSO₄ * 7 H₂O 1.0 g/l CaCl₂ * 2 H₂O 10 mg/l FeSO₄ * 7H₂O 10 mg/l MnSO₄ * H₂O 5.0 mg/l Biotin (sterile-filtered) 0.3 mg/lThiamine * HCl (sterile-filtered) 0.2 mg/l Leucine (sterile-filtered)0.1 g/l CaCO₃ 25 g/l

The CSL, MOPS and the salt solution are brought to pH 7 with aqueousammonia and autoclaved. The sterile substrate and vitamin solutions arethen added, and the CaCO₃ autoclaved in the dry state is added.

Culturing was carried out in a 10 ml volume in a 100 ml conical flaskwith baffles. Kanamycin (25 mg/1) was added. Culturing was carried outat 33° C. and 80% atmospheric humidity.

After 72 hours, the OD was determined at a measurement wavelength of 660nm with a Biomek 1000 (Beckmann

Instruments GmbH, Munich). The amount of lysine formed was determinedwith an amino acid analyzer from Eppendorf-BioTronik (Hamburg, Germany)by ion exchange chromatography and post-column derivation with ninhydrindetection.

The result of the experiment is shown in Table 1.

TABLE 1 OD Lysine HCl Strain (660 nm) g/l DSM5715 6.8 12.82DSM5715::pXK99Emobmqo 6.4 14.85

1. A process for the production of one or more L-amino acids comprisingthe following steps: a) fermenting Corynebacterium glutamicum in whichexpression of at least the endogenous mqo gene coding for malate quinoneoxidoreductase is eliminated by mutagenesis, b) accumulating at leastone L-amino acid in the medium or in the cells of the bacteria, and c)isolating the L-amino acid(s) as an end product in which optionallyportions or the entirety of the constituents of the fermentation liquorand/or of the biomass remain in the end product.
 2. The processaccording to claim 1, wherein said L-amino acid is L-lysine.
 3. Theprocess of claim 1, wherein said elimination of expression is achievedby a method of mutagenesis selected from the group consisting of: a)insertion of at least one base pair, b) deletion of at least one basepair, c) transition mutagenesis generating a stop codon, and d)transversion mutagenesis generating a stop codon.
 4. The process ofclaim 3, wherein said method of mutagenesis generates an opal stopcodon.
 5. The process of claim 4, wherein said opal stop codon is at aposition in the nucleic acid comprising the sequence of SEQ ID NO:1which codes for the tryptophan residue of position 224 of the protein ofSEQ ID NO:2.
 6. The process of claim 5, wherein said method ofmutagenesis alters said mqo gene to the sequence set forth in SEQ IDNO:3 or in SEQ ID NO:4.